Reducing the stress factor in high-energy silicon/graphite composite electrodes through systematic structuring

Summary:

The work in this poster described here, combines two methods for improving the performance characteristics of lithium-ion batteries.
On the one side, the development and application of silicon-containing active material mixtures is a promising prospect for the use in high-energy anodes. While the use of Silicon increases the energy density of the anodes due to a high specific capacity the main disadvantage of silicon is its enormous volume expansion during lithiation which can cause cracking and stability loss of the electrode. For this reason, the use of blended anodes of graphite and
silicon is a promising solution to compensate for the volume expansion of the silicon.

On the other hand, the introduction of vertically-oriented structure pores, which provide fast transport pathways for Lithium-ions can maximize the rate performance of electrodes while holding a higher energy density. The current state of research to create these cavities is laser-structuring, which has been shown to improve rate capability. However, the process sublimates the active material and the theoretical capacity of the electrode decreases. For this reason, a novel structuring process is used (additive injection) without loss of active material.

The aim in combining both methods (blend anodes and mechanical structuring) is to reduce the mechanical stress caused by the free-standing structure. High-energy lithium-ion battery anodes (8 mAh/cm²) were structured in order to create pores locally in the coating.
Experimental data from structured blend anodes with different Silicon and Graphite contents are used for the evaluation of this individual method and were compared with unstructured electrodes. First, the mechanical evaluations show that the adhesive strength increases with increasing silicon content. The reduction in strength due to the structuring process is insignificant.
In addition, the structured and unstructured electrodes were characterized in more detail with electrochemical impedance spectroscopy. The results indicate a reduction in ionic resistance and tortuosity for structured electrodes. Consequently, a better charging performance can be seen. Furthermore, the structured electrodes have a higher cycle stability, which proves the concept idea for reducing the mechanical stress by introducing free-standing spaces.